During machining of wheels of automobiles, run-out of the wheels is an important factor which affects the service lives and safety of the wheels, and therefore, run-out of the wheels is required to be detected completely. Hub manufacturers always detect the run-out of the wheels by using semi-automatic run-out detecting equipment manually, but the detecting mode has the problems of low efficiency, high labor cost, poor universality and the like. The invention provides an online wheel run-out detecting device.